1. Field of the Invention
The present invention relates to an image forming apparatus such as a laser printer or an ink jet printer, and a picture reading device applicable to the image forming apparatus.
2. Related Background Art
An image forming apparatus such as a copying machine or a laser printer includes a latent image bearing member that bears a latent image, a developing apparatus that supplies a developer to the latent image bearing member to visualize the latent image as a developer image, transferring means that transfers the developer image visualized by the developing apparatus onto a recording material to be conveyed in a given direction, and a fixing apparatus that heats and pressurizes the recording material onto which the developer image has been transferred by the transferring means under given fixing process conditions, to thereby fix the developer image onto the recording material.
Up to now, in the above-mentioned image forming apparatus, control is made in such a manner that the size or the type (hereinafter also refer to as “paper type”) of a recording paper which is the recording material is set by a user with, for example, an operation panel disposed on an image forming apparatus main body, and the fixing process conditions (for example, a fixing temperature and a conveying speed of the recording paper that passes through the fixing apparatus) are set in accordance with the set size or type of the recording paper.
Also, in the case where the recording paper is an overhead transparencies (OHT) sheet, control is made in such a manner that whether the recording paper is the OHT sheet, or not, is automatically judged by a transmission type sensor disposed inside the image forming apparatus, and in the case where a light is transmitted through the recording paper, a judgment is made that the recording paper is the OHT sheet, and in the case where the light is not transmitted through the recording paper, a judgment is made that the recording paper is a plain paper, and the fixing temperature or the conveying speed of the recording paper is set in accordance with the judgment result.
In recent years, there is an image forming apparatus in which a difference in quantity between a regularly reflected light and a diffusedly reflected light from the paper surface is detected, and the type of paper is automatically discriminated to conduct image forming control in accordance with the detected results, thereby being capable of obtaining an optimum image. FIG. 15 is a cross-sectional view showing a printer gloss meter disclosed in Japanese Patent Application Laid-open No. 11-216938. A gloss detecting device 200 has a block 240 mounted on a printed board 220. A light source tube 232 on an axis 233 and a reflection tube 214 on an axis 215 are formed in the block 240. A light source 216 is positioned in the light source tube 232. A photo sensor 222 is positioned in the reflection tube 214. In this case, the photo sensor 222 mainly reacts to a spectrally reflected light so as to discriminate a lower gloss paper and a higher gloss paper.
Also, there has been devised a method in which a CCD area sensor perceives the image on the paper surface, and a fractal dimensionality is found to obtain the relative roughness of the paper. FIG. 16 is a flowchart showing a process of the basic operation of a smoothness detecting device disclosed in Japanese Patent Application Laid-open No. 11-271037. Area irradiation onto the surface of a recording medium is performed (Step S2-1). Thereafter, a tint image formed by the reflected light of the area irradiation is read as a plain image by image detecting means including image reading means, and its tint information is detected as multivalued image data (Step S2-2). That is, the irradiated light comes to the reflected light that is tinted by concave and convex portions on the recording medium in such a manner that the concave portions are dark and the convex portions are bright, and the tint image is detected by a CCD that is the image reading means. The tint information which is the detected multivalued image data is subjected to image processing by information processing means, to thereby measure and calculate the surface roughness of the recording medium (Step S2-3). Thereafter, an image formation parameter value corresponding to the measured and calculated surface roughness is determined and controlled by image formation control means (Step S2-4). The surface roughness of the recording medium can be inferred from the tint information read from the CCD.
The surface contour of a fibrous material such as a paper has the directivity. In the case where such a surface contour of an object to be read with the directivity is measured by photographing and arithmetically operating (calculating) the surface contour, if an incident direction of the light source and a direction of the fibers are not kept constant, a variation occurs in the measured results. FIG. 9 shows a surface image in the case where a light is applied from a direction perpendicular to the fibrous direction. For example, in the case where the light is made incident perpendicularly to an angle at which the fibers of the paper are arranged as shown in FIG. 9, shadows produced by the concave and convex portions of the fibers articulately appear.
On the other hand, FIG. 10 shows a surface image in the case where a light is applied from a direction that is in parallel with the fibrous direction. As shown in FIG. 10, in the case where a light is made incident in the same direction as the fibrous direction, the shadows produced by the concave and convex portions of the fibers become weak.
As described above, there arises such a problem that the same paper surface is perceived as a different image depending on the incident direction of the light.